This invention relates generally to gas insulated electrical apparatus, and more particularly to a gas insulated transmission line having an adhesive particle trap movable with and carried by the electrostatic particle trap therein.
Gas insulated transmission lines are being used on an ever-increasing scale due to their reliability, compactness, and their ability to transmit large blocks of electrical energy economically. A typical gas insulated transmission line comprises an outer sheath of a good electrically conducting material such as aluminum, and an inner conductor disposed within the outer sheath also of a good electrical conducting material. A pressurized insulating gas, typical of which is sulfur hexafluoride at a pressure of, for example, fifty pounds per square inch gauge is utilized within the outer sheath to electrically insulate the inner conductor from the outer sheath. Insulating supports are utilized at spaced intervals along the length of the transmission line to insulatably support the inner conductor from the outer sheath. The outer sheath is typically at ground electrical potential, and the inner conductor is at high potential, typically at voltages such as 121-1200 kV phase voltage.
One of the problems which must be considered in the design of gas insulated transmission lines is the mobile conducting or semiconducting contamination particle. These particles may be present within the interior of the outer sheath and can lower the breakdown voltage of the insulating gas and possibly cause breakdown or flashover of either the gas or along the insulating supports. One means utilized in the prior art to deactivate and eliminate the deleterious effects of these contamination particles is the particle trap as described in the patent to Trump, U.S. Pat. No. 3,515,939. As illustrated in this patent, a low field region is intentionally created within the interior of the outer sheath, and contamination particles present within the outer sheath migrate to these low field regions, where the electrostatic forces exerted upon the contamination particles are reduced so that the contamination particles can no longer traverse within the interior of the transmission line.
Although the low-field particle trap has proven extremely useful in minimizing the effects of the contamination particles, certain conditions render these particle traps less effective than otherwise would be desired. For example, if the transmission line is installed on a slope, mechanical vibration on the transmission line may cause the particle previously trapped in the low field region to move away from the trap and out into the higher field areas of the system where they may cause problems. Further, if the electrostatic particle trap is movable with the support insulator which it typically protects, movement of the support insulator due to, for example, thermal expansion may cause movement of the low field region itself, thereby exposing the contamination particles previously trapped therein to be exposed to the higher fields existing outside of the trapping region.
One means which has been suggested to overcome this drawback has been to include an adhesive-coated insulating sheet in the transmission line which is attached and movable with the particle trap, so that the particle trapping region includes not only a low field region, but also an adhesive material in the low field region which also will capture contamination particles. By attaching the adhesive-coated insulating sheet to the particle trap itself, the adhesive will then be moved with the particle trap and the low field region, thus insuring that captured particles will remain in the low field regions at all times. However, what is particularly required with this type of system is some means for attaching the adhesive-coated insulating sheet to the particle trapping ring itself.